Multi-fluid cargo pumps

ABSTRACT

A submerged electrical pump for liquefied hydrocarbon gasses that is adapted for use encompassing a range of different temperatures and viscosities is disclosed. Notable elements of some embodiments of multiple fluid pumps include bearings and bearing liners made from the same material, a motor larger enough to pump the most vicious and dense fluid, extra thick bearing liners, and a trial-and-error process for choosing other pump design specifications, such as impeller wear rings, bushings, and other critical radial clearances.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit under 35 U.S.C. §119(e) of Provisional U.S. Patent Application No. 62/056,402, filed Sep. 26, 2014, the contents of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

This disclosure is directed generally to the field of processing liquefied gasses.

BACKGROUND

Liquefied hydrocarbon gasses are a commodity fuel source that are used and transported worldwide. Transportation in a gaseous state is inefficient where pipelines do not exist, so the liquid state is common for transportation, as well as storage. The liquid form of hydrocarbon gasses occupies a volume that is around 1/600^(th) of the volume occupied by hydrocarbons in the gaseous state, and the liquid form can be preserved at close to normal atmospheric pressure by keeping the temperature of the gas below its saturation temperature. Large purpose-built liquefied gas ships that can retain the necessary temperatures are typically used to transport liquefied hydrocarbon gasses. Similar liquefied hydrocarbon gas forms of trucks, smaller ships, and even storage for small communities, exist that are designed to keep LNG at the necessary temperature and pressure combination to retain its liquid state.

Pumps and expanders that are submerged in the liquid they are pumping or expanding are often used with various liquefied hydrocarbon gasses. A liquefied hydrocarbon gas is any refrigerated liquefied gas, and includes, for example, liquids with a boiling point below −0° C. at atmospheric pressure. Different hydrocarbons become liquids under different conditions of temperature and pressure, and they may also have different viscosity. Industrial facilities that produce, store, transport and utilize such gases make use of a variety of turbine-based valves, pumps and expanders (“turbomachinery”) to move, control and process the liquids and gases. Turbomachinery, which generally transfer energy between a rotor and fluid when used for liquefied hydrocarbon gasses, is often submerged in the liquid being processed. This requires the turbomachinery equipment to operate within difficult environmental conditions. In addition to very low temperature, some hydrocarbon liquids such as LNG and ammonia are also hazardous due to the possibility of fire or explosion. Submerged turbomachinery has no oxygen near the moving components, which reduces fire and explosion risk. As a result, submerged pumps and expanders have become standard tools for working with LNG, having proven it to be both safe and reliable. Such pumps and expanders have an electrical motor or generator submerged in the fluid being pumped or expanded, and the cryogenic fluid itself may be used to both lubricate and cool the machinery working on the fluid.

SUMMARY

A submerged electrical pump for liquefied hydrocarbon gasses that is adapted for use encompassing a range of different temperatures and viscosities is disclosed. Notable elements of some embodiments of multiple fluid pumps include bearings and bearing liners made from the same material, a motor larger enough to pump the most vicious and dense fluid, extra thick bearing liners, and a trial-and-error process for choosing other pump design specifications, such as impeller wear rings, bushings, and other critical radial clearances.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings wherein:

FIG. 1 is an overview of a submerged, magnetically coupled cryogenic centrifugal pump.

FIG. 2 is a cross section showing details of the lower portion of a pump, such as the pump depicted in FIG. 1.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

This disclosure presents various embodiments of liquefied hydrocarbon gas turbomachinery configured to operate with multiple fluids. Ships for transporting liquefied hydrocarbon gasses are typically designed to transport a single type of fluid, for example LNG or LPG, and the turbomachinery on such ships is often also optimized for a single type of fluid. A ship that can be easily converted from transporting one liquefied hydrocarbon to another may enable lower shipping costs, but turbomachinery is typically designed for a single fluid that has a certain viscosity and is stored at a certain temperature.

Viscosity and temperature are important in the design of turbomachinery where the fluid being pumped or expanded is used as a lubricant of the turbomachinery. Tolerances on such devices are important for low-cost maintenance, reliability, and safety. A more viscous fluid will not flow as quickly and hence may cool the turbo machinery less efficiently. As the steady state temperature of the cryogenic fluid changes, for example, from around −170° C. for LNG to around −50° C. for LPG, the components of the turbomachinery will expand or contract. The temperature range can extend from −170° C. to +50° C. for liquefied hydrocarbons, resulting in greater expansion or contraction. Measurement tolerances are small between the moving components of turbomachinery and changes in gap sizes between moving components, as temperatures change potentially from −170° C. to +50° C., requires special consideration. In addition to the steady-state temperature, the startup and shutdown processes, where temperature and pressure are changing at various points within the turbomachinery, are important design points that must be addressed for turbomachinery to operate in multiple liquefied hydrocarbon gasses.

Turbomachinery generally includes a rotor inside a stator, with a motor (for a pump) or generator (for an expander) attached to the rotor. As fluid flows through a pump or expander, the rotor rotates and the stator remains fixed. The mechanical interface between the rotor and the stator is generally the interface between a bearing and bearing liner. This interface is a critical design point for reliable turbomachinery with a long life, and bearings and bearing liners may be the highest maintenance item in turbomachinery. Such bearings between the rotor and the stator come in many types, such as traditional ball bearings, hydrostatic bearings, and hydrodynamic bearings. The types of bearings are sometimes combined in a single pump or expander, using one type of bearing at one point on the rotor, while using another type of bearing at another point on the rotor.

An embodiment of turbomachinery intended for use with multiple liquefied hydrocarbon gasses uses bearings and bearing liners that are made of the same material. Bearings and bearing liners are often made of different materials. Different materials will generally change size at different rates and will change size by different amounts for the same change in temperature. By using bearings and bearing liners made of the same material, especially where bearings lubricated by a liquefied hydrocarbon, the rate of change on both sides of a critical mechanical interface between the rotor and the stator can be matched.

FIG. 1 illustrates an overall design for a submerged (liquid and holding tank for liquid not shown), magnetically coupled liquefied hydrocarbon gas centrifugal pump 100, with the pump 100 including an inducer 102. In contrast to other types of centrifugal pumps with a horizontal rotational axis, the pump 100 is an example of a liquefied hydrocarbon gas centrifugal pump with a vertical rotational axis, which is important relative to the management and control of the movement of the shaft, as described below.

The pump 100 includes a motor 104 mounted on a motor shaft 106. Dry side ball bearings 108 support the motor shaft 106. The pump embodiment illustrated in FIG. 1 may have the motor housing 110 purged with nitrogen to remove all oxygen, to keep the spaces on the motor housing 110 inert and free from moisture, and to maintain the proper pressure balance on both sides of the magnetic coupling 112. Other mostly inert gases or fluids can also be used instead of nitrogen. The motor 104 causes the motor shaft 106 to turn. The turning of the motor shaft 106 causes a magnetic difference in the magnetic coupling 112, with the magnetic coupling 112 transferring the power from the motor shaft 106 to the pump shaft 114. The pump shaft 114 is housed within a pump housing 115 and is supported by wet side ball bearings 116. Fluid enters the pump 100 through the inlet flow 118 at the bottom of the pump 100. The fluid then goes through the various stages of an inducer 102 and an impeller 120.

The pump shaft 114 transfers the rotational power to the inducer 102 and the impeller 120. The impeller 120 increases the pressure and flow of the fluid being pumped. After the fluid goes through the impeller 120, the fluid exits through the discharge flow path 122.

The magnetic coupling 112 consists of two matching rotating parts, one rotating part mounted on the motor shaft 106 and one rotating part mounted on the pump shaft 114 next to each other and separated by a non-rotating membrane mounted to the motor housing 110. In alternative embodiments, the non-rotating membrane can be mounted to the pump housing 115. The operation of a magnetic coupling is known in the art.

While the pump 100 is illustrated having a magnetic coupling 112, embodiments are not limited to pumps with a magnetic coupling 112. Other means for transferring the rotational energy from the motor shaft 106 to the pump shaft 114 are within the scope of embodiments. Similarly, embodiments are not limited to pumps with a motor shaft 106 and a pump shaft 114. Alternative embodiments can consist of a pump with a single shaft or with more than two shafts. Also, while pump 100, as depicted, may be best adapted as a submerged retractable pump, those of skill in the art will understand that embodiments can readily be adapted to other types of pumps, such as removable, external, and emergency liquefied hydrocarbon gas pumps. Embodiments can also be readily applied by those skilled in the art to other types of turbomachinery, such as liquefied hydrocarbon gas expanders.

The pump 100 uses a thrust equalizing mechanism (TEM) device 124 for balancing hydraulic thrust by using a portion of the input fluid flow to balance the generated thrust forces as well as lubricating the ball bearing for the turbine shaft. The TEM is depicted in more detail in FIG. 2. A TEM can be used to reduce maintenance cost and increase lifetime by balancing axial loads, especially through startup and shutdown of a submerged pump or expander. Surviving a fast change in temperature and pressure during the startup and shutdown of turbomachinery may be even more important than designing for steady state temperature for reliability and low maintenance costs. It is well known that the lifetime and maintenance costs of submerged pumps and expanders are largely determined by the number of startup and shutdown cycles the turbomachinery is put through, so designs such as a TEM that account for startup and shutdown can be advantageous.

The TEM device 124 ensures that the wet side ball bearings 116 are not subjected to axial loads within the normal operating range of the pump 100. The wet side ball bearings 116 are lubricated with the fluid being pumped. When using the fluid being pumped for lubrication, it is imperative that the axial thrust loads are balanced to prevent vaporization of the fluid in the bearings, thereby ensuring reliability. Axial force along the pump shaft is produced by unbalanced pressure, dead-weight and liquid directional change. Self-adjustment by the TEM device 124 allows the wet side (product-lubricated) ball bearings 116 to operate at near-zero thrust load over the entire usable capacity range for pump 100. This consequently increases the reliability of the bearings. The TEM device 124 increases the reliability of the various components of the pump such as the impeller and inducer, and also reduces equipment maintenance requirements. Alternative embodiments of liquefied hydrocarbon gas pumps may not include the TEM device 124.

FIG. 2 depicts a cross section of wet bearings and a TEM system, such as might be implemented in the lower portion of pump 100 in FIG. 1. Impeller 202 is attached to, and spins with, rotor 204. The impeller 202 and rotor 204 rotate within the fixed stator 200. As the impeller 202 spins, fluid enters 220 from the bottom of the pump or expander, is forced through the impeller 202 and most of the fluid exits at 218. A small portion is leaked 220 after passing out of the highest pressure impeller or runner stage. The leaked 220 portion squeezes through the fixed orifice 212 between the upper wear ring 208 and the impeller 202. This leaked 220 portion of the pumped or expanded fluid is used to lubricate the bearings 250 and provide the force necessary for the thrust balancing mechanism of the TEM. The lower wear ring 206 or bushing is smaller in diameter than the upper wear ring 208, which creates a force in the upward direction. Due to this upward force, the pump shaft and all of its rotating components move upward. This upward movement reduces the gap between the impeller and the stationary thrust plate 210, thus restricting the leakage through the variable orifice 214. When the outflow is restricted through the variable orifice 214, pressure builds in the upper chamber 222 until the pressure is sufficient to create a downward thrust that balances the previously mentioned upward thrust on the rotor. If the downward thrust from the pressure in the upper chamber 222 were to grow larger than the upward thrust, the rotor would move down slightly and open the variable orifice 214 which would allow the pressure in the upper chamber 222 to reduce by way of increased flow through the variable orifice 214. The end result is an equilibrium created between the upper and lower impeller surface to provide a stable system with little or no axial thrust load on the bearings 250.

After leaking through the variable orifice 214 and balancing the vertical thrusts, the leaked 200 fluid then also lubricates the bearings 250 by allowing a small about of fluid between the bearing 250, the outer wear ring 254, and the inner wear ring 252. The fluid leaked past the bearing 250 can then be returned 216 back to join the low pressure fluid after exiting at 218.

When designing any liquefied hydrocarbon gas pump the spacing tolerances at the fixed wear rings (upper wear ring 208 and lower wear ring 206) and the bearings 250 are important. Of particular importance for designs to handle multiple fluid types and hence multiple temperatures is the tolerance at the bearings 250. By matching the material of the bearings 250 and with the material of its liners (inner bearing liner 252 and/or outer bearing liner 254), the variation in gaps can be minimized.

To accommodate multiple cryogenic fluids, additional changes can be made to turbomachinery initially designed for a single liquefied hydrocarbon gas. The motor (for a pump) or generator (for an expander) must generate or accept enough torque to handle the highest density fluid that will be run through the turbomachinery. In addition, the thickness of the bearing liners may be made thicker than is necessary for whichever type of material is used for turbomachinery designed for a single fluid. A wider range of operating temperatures causes the turbomachinery housing to shrink and expand more, which puts more pressure at the bearing/liner junction. A thicker bearing liner can be able to withstand the greater pressure from the larger variations in temperature. In an embodiment, the inner bearing liner and the outer bearing liner may be made thick enough to prevent liner material yielding under the pressure applied to the outer liner surface at the coldest potential operating temperature.

While this document contains many specifics, these should not be construed as limitations on the scope of an invention or of what may be claimed, but rather as descriptions of features specific to particular embodiments of the invention. Certain features that are described in this document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be exercised from the combination, and the claimed combination may be directed to a subcombination or a variation of a subcombination. 

What is claimed:
 1. Turbomachinery for multiple liquefied hydrocarbon gasses, comprising: a bearing at an interface between a rotor and a stator; an inner bearing liner affixed to the rotor; an outer bearing liner affixed to the stator; and wherein the bearing, the inner bearing liner, and the outer bearing liner all consist of the same material; the bearing is disposed between the inner bearing liner and the outer bearing liner; and the bearing is lubricated with one of the multiple liquefied hydrocarbon gasses.
 2. The turbomachinery of claim 1, wherein the inner bearing liner and outer bearing liner each comprise a thickness that is thick enough to prevent at least one of the inner bearing liner or the outer bearing liner from yielding under pressure applied to an outer liner surface at a coldest potential operating temperature.
 3. The turbomachinery of claim 1, wherein at least one of a thickness of at least one of the inner bearing liner or the outer bearing liner, or a size of the bearing is determined based on expansion or contraction of the same material under varying temperature conditions or varying pressure conditions associated with the multiple liquefied hydrocarbon gasses.
 4. The turbomachinery of claim 3, wherein the varying temperature conditions are based on different boiling points of the multiple liquefied hydrocarbon gasses.
 5. The turbomachinery of claim 1, wherein the same material of the bearing, the inner bearing liner, and the outer bearing liner reduces variation in gaps between the bearing, the inner bearing liner, and the outer bearing liner due to temperature variation of the multiple liquefied hydrocarbon gasses.
 6. The turbomachinery of claim 1, further comprising: a thrust equalizing mechanism that directs the one of the multiple liquefied hydrocarbon gasses to flow around and lubricate the bearing.
 7. The turbomachinery of claim 6, further comprising: a lower wear ring disposed on the stator; and an upper wear ring disposed on the stator; wherein the thrust equalizing mechanism is disposed between the lower wear ring and the upper wear ring; and wherein at least one of a thickness of the lower wear ring or the upper wear ring, or a material of the lower wear ring or the upper wear ring is selected based on the same material of the bearing, the inner bearing liner, and the outer bearing liner.
 8. The turbomachinery of claim 7, wherein at last one of the thickness of the lower wear ring or the upper wear ring, or the material of the lower wear ring or the upper wear ring is selected based on a temperature tolerance associated with the same material of the bearing, the inner bearing liner, and the outer bearing liner.
 9. The turbomachinery of claim 7, wherein the material of the lower wear ring and the upper wear ring comprises the same material of the bearing, the inner bearing liner, and the outer bearing liner.
 10. The turbomachinery of claim 1, wherein the bearing comprises at least one of a ball bearing, a hydrostatic bearing, or a hydronamic bearing.
 11. Turbomachinery for use with multiple liquefied hydrocarbon gasses, comprising: a liquid chamber configured to direct flow of one of the multiple liquefied hydrocarbon gasses within a stator of the turbomachinery; and one or more bearing assemblies at an interface between a rotor and the stator, wherein the one or more bearing assemblies consist of a first material, and wherein the one or more bearing assemblies contact the liquid chamber, such that the one of the multiple liquefied hydrocarbon gasses lubricates the one or more bearing assemblies.
 12. The turbomachinery of claim 11, wherein the one or more bearing assemblies each comprise: a bearing; an inner bearing liner affixed to the rotor; and an outer bearing liner affixed to the stator, wherein the bearing is disposed between the inner bearing liner and the outer bearing liner.
 13. The turbomachinery of claim 12, wherein the inner bearing liner and outer bearing liner each comprise a thickness that is thick enough to prevent at least one of the inner bearing liner or the outer bearing liner from yielding under pressure applied to an outer liner surface at a coldest potential operating temperature.
 14. The turbomachinery of claim 11, wherein a thickness of the one or more bearing assemblies is configured to withstand expansion or contraction of the first material under varying temperature conditions or varying pressure conditions associated with the multiple liquefied hydrocarbon gasses.
 15. The turbomachinery of claim 14, wherein the varying temperature conditions are based on different boiling points of the multiple liquefied hydrocarbon gasses.
 16. The turbomachinery of claim 1, further comprising: a thrust equalizing mechanism that directs the one of the multiple liquefied hydrocarbon gasses to flow around and lubricate the one or more bearing assemblies.
 17. The turbomachinery of claim 16, further comprising: a lower wear ring disposed on the stator; and an upper wear ring disposed on the stator; wherein the thrust equalizing mechanism is disposed between the lower wear ring and the upper wear ring; and wherein at least one of a thickness of the lower wear ring or the upper wear ring, or a material of the lower wear ring or the upper wear ring is selected based on the first material of the one or more bearing assemblies.
 18. The turbomachinery of claim 1, wherein the one or more bearing assemblies each comprise at least one of a ball bearing, a hydrostatic bearing, or a hydronamic bearing.
 19. A method for designing a turbomachinery for use with multiple liquefied hydrocarbon gasses, comprising: selecting a motor or a generator capable of providing a torque, wherein the torque is determined based on a highest density of the multiple liquefied hydrocarbon gasses, and wherein the motor or the generator is rotationally connected to a rotor; and selecting at least one bearing, an inner bearing liner, and an outer bearing liner for placement between the rotor and a stator based on the multiple liquefied hydrocarbon gasses, wherein the at least one bearing, the inner bearing liner, and the outer bearing liner are made of the same material, and wherein the at least one bearing is lubricated by one of the multiple liquefied hydrocarbon gasses.
 20. The method of claim 19, further comprising: selecting a material of at least one of a wear ring or a bushing disposed on an interior of the stator of the turbomachinery based on the same material of the at least one bearing, the inner bearing liner, and the outer bearing liner. 